1. Field of the Present Invention
The present invention relates to a power module substrate having a heatsink, which is employed to a semiconductor device controlling a large amount of electrical current and high voltage, a method for manufacturing the same, a power module having a heatsink, and a power module substrate.
This application is based on and claims priority from Japanese Patent Application No. 2008-67344, filed on Mar. 17, 2008 and Japanese Patent Application No. 2008-234997, filed on Sep. 12, 2008, the contents of which are incorporated herein by reference.
2. Background Art
Conventionally, a power module substrate having a heatsink, which is employed to a semiconductor device controlling a large amount of electrical current and high voltage, is known.
As this kind of the power module substrate, a structure in which a circuit layer composed of aluminum is formed on one face (a first face) of an insulating substrate, a metal layer composed of aluminum is formed on the other face (second face) of the insulating substrate, and a top panel portion of the heatsink is connected to a surface of the metal layer is widely proposed.
The foregoing power module substrate is shown in, for example, Japanese Patent Publication No. 3171234 and Japanese Unexamined Patent Application, First Publication No. H10-065075.
The foregoing power module having a heatsink is manufactured so that the power module substrate is connected to the heatsink, after the power module substrate is formed by connecting the power module substrate, the insulating substrate, the circuit layer, and the metal layer together.
In the power module substrate having a heatsink, electronic components such as a semiconductor chip are connected to the circuit layer by use of a solder.
However, in the above-described power module substrate having a heatsink, if total thickness of the metal layer and the top panel portion of the heatsink which are positioned on the second face of the insulating substrate is small, the bending rigidity thereof is degraded, and warpage may occur thereon.
In recent power modules having a heatsink, the size and thickness thereof have been reduced, but, the amount of heat generated in an electronic component has a tendency to increase.
A heatsink in which the thickness of the top panel portion is small is employed in order to improve the cooling efficiency of the heatsink.
Consequently, the total thickness of the metal layer and the top panel portion of the heatsink which are positioned on the second face of the insulating substrate become small, there is a problem in that the above-described warpage occurs.
In addition, in the power module having a heatsink disclosed in Japanese Patent Publication No. 3171234, a metal layer is connected to a heatsink via aluminum foil, and a melting point lowering layer composed of an Al—Si series brazing filler metal being formed on both faces of the aluminum foil.
Because of this, portions including a great amount of Si and having a high degree of hardness are formed at the joint interface between the aluminum foil and the metal layer and the joint interface between the aluminum foil and the heatsink.
In the case where the portions having a high degree of hardness are formed at the metal layer and the heatsink which are positioned on the second face of the insulating substrate as mentioned above, the metal layer or the top panel portion of the heatsink is restrained at the portions having a high degree of hardness.
For this reason, for example, when the power module substrate is connected to the heatsink, even if a pressure is applied in the stacking direction thereof, the metal layer is restrained by the portions having a high degree of hardness, it is not sufficiently deformed, and warpage cannot be suppressed.